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[PAUTHABIELF64] Remove alternative ELF marking scheme #250

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Jul 2, 2024
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[PAUTHABIELF64] Remove alternative ELF marking scheme #250

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46 changes: 7 additions & 39 deletions pauthabielf64/pauthabielf64.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -236,7 +236,9 @@ changes to the content of the document for that release.
| | | DT_AARCH64_VARIANT_PCS. |
+------------+-----------------------------+------------------------------------------------------------------+
| 2024Q1 | 29\ :sup:`th` January 2024 | Update preferred ELF marking scheme to be GNU property based |
| 2023Q4 | 18\ :sup:`th` March 2024 | Update relocation codes to move out of private experiments space.|
| | 18\ :sup:`th` March 2024 | Update relocation codes to move out of private experiments space.|
| | 19\ :sup:`th` March 2024 | Remove alternative ELF marking scheme. No implementation is |
| | | using it. |
+------------+-----------------------------+------------------------------------------------------------------+

References
Expand Down Expand Up @@ -852,13 +854,6 @@ This document defines the core information that any ELF marking
scheme must contain and the base compatibility model that uses that
information.

The default ELF marking scheme uses the Program Property note format
defined in (`LINUX_ABI`_). An alternative encoding that uses a Arm
defined Note section called ``.note.AARCH64-PAUTH-ABI-tag`` is defined
for platforms that do not support Program Properties, or have legacy
binaries from earlier versions of this specification. This is described
in `Appendix Alternative ELF Marking Using SHT_NOTE section`_.

Core information
----------------

Expand Down Expand Up @@ -922,15 +917,10 @@ Base Compatibility Model
A per-ELF file marking scheme permits a coarse way of reasoning about
compatibility.

* All reasoning about compatibility is done using the `Core Information`_.
This permits an ELF file using the ``.note.gnu.property`` ELF marking to
be compared to an ELF file using the ``.note.AARCH64-PAUTH-ABI-tag`` ELF
marking.

* If an ELF file contains multiple ELF markings of the `Core
Information`_, for example it contains both a ``.note.gnu.property``
section and a ``.note.AARCH64-PAUTH-ABI-tag`` section, then all
must encode the same `Core Information`_.
* All reasoning about compatibility is done using the `Core
Information`_. This permits an ELF relocatable object file using
the ``.note.gnu.property`` ELF marking to be compared to an ELF file
using build attributes that encode the `Core Information`_.

* The absence of any ELF marking means no information on how pointers
are signed is available for this ELF file. When used in combination
Expand Down Expand Up @@ -1282,25 +1272,3 @@ Some observations:
* When not dynamic linking a static linker may choose to encode the
pointer signing information in a custom encoding understood by the
start-up code used.

Appendix Alternative ELF Marking Using SHT_NOTE section
=======================================================

A new section named ``.note.AARCH64-PAUTH-ABI-tag`` of type
``SHT_NOTE`` is defined. This section is structured as a note section
as documented in SCO-ELF_, and its attribute flag ``SHF_ALLOC`` must
be set.

The ``namesz`` field shall be 4

The ``descsz`` field shall be 16. See ``desc`` below.

The type field shall be ``NT_ARM_TYPE_PAUTH_ABI_TAG``, defined to the
value 1.

The ``name`` field shall be the null-terminated string ``ARM``.

The ``desc`` contain 2 64-bit words. With the first 64-bit word being
the ``platform identifier``, and the second 64-bit word being the
``version number``. Both of these form the information required in
`Core Information`_ above.
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